1. Field of the Invention
This invention relates to an improved method for preparing filaments and fibres of a prevalently cellulosic nature and more precisely filaments and fibres (and textile products made of said filaments and fibres) of regenerated cellulose (viscose rayon) produced by wet spinning in an acid bath alkali-cellulose treated with carbon sulfide, which filaments, fibres and other products exhibit a high resistance to combustion and when maintained under conditions of incandescence.
2. Description of the Prior Art
Many attempts have been made in the art to improve the resistance to combustion of textile products made of rayon viscose fibres, and various techniques have been proposed and industrially adopted for this purpose. The large number of patent and technical publications concerning such techniques makes it unnecessary to describe them in detail, except insofar as this may be useful to the understanding of this invention. Therefore no reference to techniques involving the application of flame proofing additives to the surface of cellulosic yarns or to fabrics made therefrom and the penetration of said agents to some extent into said products.
The improvement which forms the object of this invention relates to the method for introducing the flame proofing additive (generally a compound or a combination of compounds containing phosphorus and nitrogen) into the spinnable viscose dope prior to spinning it and even immediately before this, viz, in correspondence of the spinning nozzles, whereby the flame proofing additive becomes more or less homogeneously dispersed throughout the cross-section of the resulting fibres. Some of these techniques comprise the use of liquid additive which are insoluble in the dope (see for instance U.S. Pat. No. 3,455,713) or the use of solid or semi-solid additives, in particles of microscopic dimensions, also insoluble in the dope (see for instance U.S. Pat. No. 3,645,936).
An important progress in the art has been provided by the applicant through the invention described and claimed in previous Italian Pat. No. 969954 (which corresponds to Belgian Pat. No. 806504 and to patent application publication Nos. 73.38109 in France and F 23 53 821.8 in Germany), which patents and publications are incorporated herein by reference, and which, among other things, critically and analytically describe the previous state of the art.
In said previous proposal of the applicant, an advantageous operating procedure had been disclosed, according to which a compound of phosphorus and nitrogen is dissolved in an amount of the aqueous solvent of the cellulose xantogenate, under correspondingly alkaline conditions, so that it becomes "cospinnable" with the viscose and constitutes therefore with said viscose, a spinnable dope which is at least physically homogeneous. Further, said compound becomes solid in the spinning and coagulating bath through a process parallel to the regeneration of the cellulose and gives rise into insoluble submicroscopic particles dispersed and stably bound in the cross-sections of fibre produced, so that it is practically impossible to extract them even by the most severe and repeated mechanical and chemical treatments, such as repeated washings, and so forth.
Said previous proposal of the applicant has been carried into practice and industrially applied by using as the flame proofing compound, tetra-kishydroxymethylphosphonium chloride, added to the viscose dope in the form of an alkaline aqueous solution, preferably including carbon sulphide and brought to a pH close so that of the cellulose xantogenate solution.
The resulting composite dope, consisting of cospinnable and co-coagulatable cellulosic and phosphonic components, produces fibres having the most desirable properties, which are not attained concurrently by any other means known in the art of high resistance to combustion, stability of said resistance in time, under treatments and in use, and luster and substantial trasparence equal to that of a normal fibre.
The aforesaid phosphonic compound however has the serious and industrially highly relevant drawback, of being very costly and complicated to prepare and is therefore limited to use for special productions and for the manufacture of highly priced products, such as artificial furs, and a few others.
Other known flame proofing additives and compounds, for instance those in which the base phosphorus compound is a halide, in particular a phosphonitrile chloride, which are available and can be manufactured more economically, are not suited, as far as is known in the art, to be added to the spinning dope to form, as the aforesaid previous invention requires, an essentially homogeneous mixture of cospinnable and co-coagulatable cellulosic and phosphonic components, capable of becoming insoluble the wet spinning, through parallel chemical transformations.